Continuous soapmaking



April 29, 1952 L. A. LEDGETT con'rmuous SOAPMAKING 4 Sheets-Sheet 1 Filed Dec. 22, 1944 April 29, 1952 L. A. LEDGETT CONTINUOUS SOAPMAKING 4 Sheets-Sheet 2 Filed Dec. 22, 1944 INVENTOR Lowzu. A- LEDGETT 4W A ORNEY April 9, 1952 L. A LEDGETT 2,594,461

CONTINUOUS SOAPMAKING Filed Dec. 22, 1944 4 Sheets-Sheet 3 INVENTOR LOWELL A. LEDGE T TTORNEY April 2 .L. A. LEDGETT CONTINUOUS SOAPMAKING 4 Sheets-Sheet 4 Filed Dec. 22, 1944 wow Q INVENTOR LowEu. A. LEDGETT TTQRNEY Patented Apr. 29, 1952 CONTINUOUS SOAPMAKING Lowell A. Ledgett, Ridgewood, N. J., assignor to Colgate-Palmolive-Peet Company, Jersey City, N. J., a corporation of Delaware Application December 22, 1944, Serial No. 569,343

6 Claims. 1 The present invention relates to an apparatus for and a method of making soap and, more particularly, to an apparatus for and method of making soap continuously.

In the most widely practiced commercial method of making soap, fats and oils in the form of 1 glycerides have been saponified batchwise with caustic soda or other saponifying agent in large kettles. The mixture of fat and caustic was heated and agitated during the reaction in the kettle which resulted in the formation of soap and glycerineJ When the reaction was completed salt was, added, causing rough separation of the reaction mass into an upper soap layer and a lower layer comprising glycerine, salt and water. The crude glycerine solution and the soap were then processed separately.

The batch process of making soap has many recognized disadvantages, among which are the following: the process is slow; the equipment necessarily is large in proportion to the output; accurate control of the process is very diflicult or impossible; highly skilled soap boilers must be employed to supervise the boiling operation; and glycerine is obtained in an impure, dilute solution which requires extensive refining and concentration before it is acceptable as an article of commerce.

Numerous proposals have been made to carry out the saponification reaction by a continuous method in order to avoid one or more of these recognized disadvantages of the batch process. While differing in details, the various proposals have certain features in common, including supply vessels for saponiflable material and the saponifying agent, pipes connecting these supply vessels to a mixing device or reaction chamber, and an outlet line from the chamber for removal of the reaction mixture. Means for controlling the flow of the saponifiable material and the saponifying agents into the reaction chamber are required. In the early proposals for continuous soap making apparatus, manually operated valves in the feed lines were suggested, but ex- .perience proved this to be an unsatisfactory and vide a system that was capable of producing soap .of uniform, constant, desired free alkali content.

One reason for this failure is that no provision has been made for maintainingthe temperature of the reactants constant during volumetric proportioning. The continuous saponification of fatty material to produce soap with free alkalinity of say 0.10% as Nazo within close limits requires that the fatty material and alkali solution be introduced into the reaction chamber in a definite weight ratio which is fixed by the saponiflcation value of the fatty material and the concentration of the alkali solution. Continuous proportioning devices which operate on volumetric rather than gravimetric basis are inherently incapable of effecting gravimetric proportioning of fluids which vary in relative temperature, and where the coeflicient of cubic expansion of one fluid differs appreciably from that of another, volumetric proportioners cannot effect gravimetric proportioning under varying temperature conditions even though the temperatures of one fluid follow closely the temperature changes of the other fluid.

It is a feature of the present invention to maintain the temperature of each of the fluids being proportioned by volumetric proportioning substantially constant during proportioning.

A second reason for the failure of prior proposed continuous soap making systems to produce soap of uniform desired composition is that where the flow of streams of fluids is controlled by automatic proportioning devices, the proportionality of feed rates of the streams is subject to cyclic variation, and even though the ratio of the volume or Weight of one fluid to the volume or weight, respectively, of the other fluid averaged over the period of cyclic variation could be maintained substantially constant, the ratio of alkali to fatty material in increments of the combined streams would vary, and in prior proposed systems this variation persisted through tothe finished soap.

It is another feature of the present invention to provide for the averaging out of cyclic variations in the proportionality of feed rates.

A third reason for the failure of prior proposed continuous soap making systems to produce soap of constant desired compositions is that proportioning devices cannot take into account variations in the saponification value of the fatty material and/or the concentration of alkaline solutions.

It is a further feature of the present invention to provide for continuous or periodic automatic reset of proportionality of feed rates as necessitated by such variations, or any other variations which result in a deviation of the free alkali content of the soap from the desired value, utilizing as the motive force a generated electrical potential which is related to the free alkali content of the soap produced.

The present invention also makes provision for avoiding the difficulties resulting from mild premixing of the fatty acids and a saponifying agent such as formation of soap curds having fatty material and caustic separately occluded in the soap whereby complete neutralization is prevented unless these curds are broken up so as to bring the occluded fatty material and caustic into contact. By the present process the formation of such objectionable curds is prevented by subjecting the fatty acids and caustic to violent disruptive agitation substantially as soon as they have been contacted, this contact preferably being effected by dispersing the reactants in a soap of proper fluidity attained by control of free alkalinity, temperature and moisture content.

Other objects, features and advantages of the present invention will become apparent from a perusal of the following detailed description. It is to be understood that the various features of the invention may be employed singly or in combination and that the embodiments of the invention specifically illustrated in the drawings and described hereinafter are given for the purpose of illustrating, but not limiting, the scope of the invention as defined in the appended claims.

In the drawings:

Fig. '1 is a diagrammatic layout of a continuous soap making system;

Fig. 2 is 'a'schematic layout of a modified continuous soap making system;

Fig. 3 shows a schematic layout of a modified system for heating the reactants;

Fig. 4 represents a fragmentary, schematic layout of a modified form of continuous soap making system adapted to feed a proportioned amount of an additional ingredient into the soap stream, and

Fig. 5 is a fragmentary, vertical, sectional view through 'a contactor adapted to carry out the saponification reaction in accordance with the present invention.

Referring now more particularly to Fig. 1, the apparatus comprises supply tanks 2 and 4 for fatty material and alkali -solution, respectively. Pipe lines 6 and 8 lead from the tanks 2 and 4 to the inlet side of circulating pumps in and I2, respectively. Connected to the outlet side of the circulating pumps are pipes I4 and [6 connected, respectively, with heaters l8 and 20. The outlet side of the heaters are connected, respectively, with Ts 22 and 24. One branch of T 22 is connected to a return pipe 25 provided with a valve 26 and T 24 is similarly connected to a return pipe 21 having a valve 28 therein. Each of these return pipes extends adjacent to the bottom of the supply tank and terminates at a nozzle in the throat of an eductor 29 for mixing the tank contents.

The other branch of each T is connected, respectively, to feed lines 30 and 32 connected in series with feed pumps 34 and 36 and a proportioning device 38.

Tanks 40 and 42 mounted on beam scales 44 and 46 are connected through the pipes 48 and 50, respectively, with feed lines 30 and 32 through 3-way valvesg52 and 54. Scale tank 40 is connected by pipe 56 with supply tank 2 and scale tank 42 is similarly connected by means of pipe 58 with supply tank 4.

The feed lines 30 and 32 leaving the proportioner 38 are connected with a contactor 60 where the fatty material and alkali solution are mixed together under such conditions as to cause them to react to form soap which flows from the contactor through a line 6 I. As will be described more fully hereinafter, the fatty acids and alkali are not premixed before entering the contactor where they are highly dispersed in the reaction product, which serves as an autocatalyst for the saponification reaction, and they are retained long enough under conditions of intimate contact for soap to form by quantitative neutralization or saponification.

Means designated by reference numeral 62 for generating an electrical potential related to the free alkali content of the soap is associated with the soap line 6|. The potential generating means 62 is electrically connected by a line 63 to a suitable potentiometer controller 64 which regulates through an electrical, peneumatic or hydraulic system 65 on adjusting means 66 on the proportioning device 38 to maintain the free alkali content of the soap within predetermined narrow limits.

The heaters I3 and 28 may be of any desired type and, although they are illustrated in the drawing as being of the same type, it will be understood that different types may be employed. The heater illustrated in the drawing is of the fin tube type connecting with a source of steam through a steam line 10 and having a withdrawal line 12 for the condensate. The steam line i0 is provided with a control valve 14 which may be of the diaphragm air operated type as shown. v

Mounted in each of the Ts 22 and 24 is a primary temperature measuring instrument (6, e. g., a mercury filled bulb, a thermocouple, or the like, operatively connected through line '18 with a suitable temperature controller 80, which may be of the air operated type as illustrated or any other desired type. In the type illustrated, the temperature controller is provided with an air supply line 82 and a connection 84 with the diaphragm valve 14. In the operation of the apparatus illustrated in Fig. 1 the temperature of the fatty material and the caustic solution during volumetricproportionihg "can be controlled and maintained substantially constant and thereby eliminate variation in the gravimetric feed ratio of the .two reactants. This is an important feature of the present invention where a volumetric proportioning device is employed.

The operation of the heating unit is the same for both the fatty material and the caustic solution and a description of one will suffice. The supply tank 2 is filled to a desired level 'with the fatty material from a storage tank of larger capacity. The circulating pump I!) isstarted and this causes a flow of the fatty material from the tank 2 through the pipes 6, l4, the heater l8, the T 22 and the return pipe 25, valve '26 being open. The introduction of the returning fat into eductor 29 sets up a circulation of the fatty material within the supply tank '2, thereby keeping the entire supply of fat in the tank 2 at substantially constant and uniform temperature throughout. Steam is admitted through diaphragm valve 14 into the heater is in controlled amounts so as to raise the temperature of the fat pa'ssingthrough the heater to the desired tem- "perature and this is automatically controlled by the temperature controller 80 in a manner well understood by those skilled in the art.

Thequantity of fat circulating in the manner described may be considerably greater than the amount withdrawn from the T 22 by the feed pump 34, thu insuring that the temperature of the fatty material being pumped to the proportioning device 38 will be maintained substantially constant notwithstanding rapid substantial changes in the feed rate. Where the feed rate is relatively constant and tank 2 is supplied continuously from the storage tanks, the quantity of fat circulated may be reduced. Valve 26 permits regulation of the fat recirculatio rate from zero to a maximum. Valve 28 function is like manner in the caustic system.

In bringing the apparatus into operation after the fat and alkali in tanks 2, and 4 have been brought to the predetermined temperature, the 3-way valves 52 and 54 are turned so as to divert the stream of fatty material and caustic solution into their respective scale tanks. In this way the volumetric proportioning device 38 can be set so as to feed the alkali at exactly the proper flow rate ratio completely to saponify the fatty material and leave the desired free alkali in the soap product and this ratio can be established without wasting any of the ingredients. As soon as the proper rates and ratio of flow have been established, the 3-way valves 52 and 54 are turned to direct the streams into the contactor 80.

Fig. 2 shows another system for feeding fatty acids and alkali to the volumetric proportioning device at controlled temperature. While somewhat simpler than the system illustrated in Fig. 1, it is preferred because it requires a minimum of equipment to accomplish the essential functions of this feature of the invention. In this embodiment of the invention, the storage tanks for fatty material and caustic solution, respectively, are represented by referenc numerals 86 and 88. These are preferably large yard storage tanks from which fat and alkali are .pumped by submerged pumps 90 and 92, respectively, through pipes 94 and 96, without intermediate storage, into small tanks 98 and I00 mounted on scales I02 and I04. Return lines I06 and I08 are connected through valves 52 and 54 with the feed lines 30 and 32 and lead back to the storage tanks 86 and 88. Means are provided for maintaining the head in tanks 98 and I00 substantially constant, e. g., float control regulation of pumps 90 and 92 or overflow return of excess supply to the storage tanks as illustrated by lines I01 and I09.

In the system illustrated in Fig. 2, separate pumps for recirculation and feed are not employed, the single pumps I0 and I2 serving both functions in the fat supply system and alkali supply system, respectively. Recirculation at a large rate compared to the feed rate is advantageous during operation where feed rates change, whether purposely or unavoidably, or where the heat transfer duty is subject to wide variation, e. g., variation due to appreciable changes in the temperature of the raw stock supply from the storage tank. In continuous operation under fairly steady operating conditions such as are practicable to obtain in the system of Fig. 2, the feed rate will be large compared to the recirculation rate and the recirculation rate may, insome cases, be reduced to zero.

In starting up the operation of the apparatus illustrated in Fig. 2, the tanks 98 and I00 are filled tothe desired level by operating the pumps:

vided for calibration of the proportioner.

and 92, after whichthese pumps are temporarily stopped. With valves 26 and 28 open and valves 52 and 54 closed, pumps I0 and I2 are started and steam'is supplied to the heaters I8 and 20 to bring the temperature of the fatty materials and alkali solution to the desired point. Valves 52 and 54 are then turned so as to direct the flow of material into the return lines I06 and I08 and the proportioning device 38 is adjusted so as to control the relative rates of flow properly to produce a soap of desired free alkali content. The rate of flow of the fatty material and alkali solution from the respective tanks 98 and- I00 is readily checked by the decrease in weight measured on the scales I02 and I04. As soon as the proper rates and ratio of flow are established, the valves 52 and 54 are turned to direct the materials into the contactor 60 and the submerged pumps .00 and 92 are started again to keep the proper supply in tanks 98 and I00,

An alternate system of fixing the feed temperature of the fatty material and/or alkali solution is to heat the entire supply in a tank IIO to a controlled temperature by the means shown in Fig. 3. The tank may be mounted on a scale as are tanks 98 and I00 in Fig. 2, or separate scale tanks such as 40 and 42 of Fig. 1 may be pro- The means for circulating the fluid to be heated comprises an outlet pipe II2, a T H4, one branch of which is connected with the circulating pump I I6 which pumps the fluid through the pipe II8 to the heater I20 and through a return line I22 back into the supply tank H0. The heater comprises a steam supply line I24, a condensate line I26, a diaphragm valve I28 and a temperature controller I30. The primary temperature measuring device I32 is mounted in the T H4 and is operatively connected with the temperature controller I30 through the line I34. The temperature controller is of the same type illustrated in Fig. 1 comprising an air line I36 and a connecting line I38 to the valve I28. The other branch of the T is connected to the feed line I40 through a feed pump I42 Many modifications of the heating and temperature control system are possible and, in these various well known forms, have been practiced for other purposes but not as an essential control to make continuous volumetric proportioning quantitatively equivalent to gravimetric proportioning. Depending on the net effect of the several factors influencing this result, the preferred heating and temperature control system will take any of the illustrated forms, combinations thereof, or others well known. In the system illustrated in Fig. 3 greater stability of controlled temperature is obtained by interposing the total heat capacity of the tank contents between the heater and feed stream, whereas temperature stability is diminished at an increase in flexibility of tank usage by taking the feed stream 01f the recirculation stream as in Fig. 1 and Fig. 2. Sufiicient recirculation, however, will assure adequate stability when using standard air operated temperature controllers. Under ideal conditions 01' steady state flow and heating duty, the recirculation may be eliminated and feed temperature controlled to within il F. with standard equipment installed so as to minimize time lag. All

systems illustrated have been found to give satis- [factory' results in practice, but ordinarily the system illustrated in Fig. 2 is preferred and recirculation is discontinued once steady operation has'beeniattained. l

I In general, the controlled temperatures of the fatty material and alkali solution are set-so that after release of 'heat of neutralization and heat of stirring the soap temperature'will bethat preferred to give the desired fiuidi ty'at-a given soap moisture content.

The pro'portioning device 38 may be any desired type. As those skilled in the artknow, several types of volumetric proportioner's havebeen developed, including proportioning meter systems such as the Askania orifice meter system, the Bowser positive displacement meter system with throttling control, the Prdpjortioners. Inc. 70,

positive displacement meter system with controlled displacement, and 'propo'rtioni'ng pump systems, such as the Hills-McCann'a system, 'with speed or displacement c'ont'rolof the'pumps. -Any of these systems'm'ay be used as the p'ropor tioner in the present invention, as well as any other volumetric proportioningdevice which hasmeans for varying and controlling the feed rate ratios. It is also within the contemplation of the invention to employ a 'gravimetric propoxtione'r, e. g., the Proportioners, Inc. Loss-In Neig ht scales with controls for gravimetric propo'rtiom value of the fatty materialand theconcentration I of the alkali solution. 'When-using a volumetric type proportioner, it must be set while the feed. streams are at the desired temperature for the reactants, and by maintaining "the temperature of the feed streams during operation at substantially this desired value, 'it is possible to introduce into the contactor 50 an amount of caustic suficient completely to saponifythe fatty material "and leave adeSiredeXcesscaustic, e. g.,

about 0.10% as NazO,"a's averaged'over the period I of cyclic variation of the 'proportio'ning device. The same result is obtained using a gravimetric type of proportioner without-accurate temperature control of the feed streams.

In order to assure complete saponi'ficationwithin'a short period 'of time, it is necessary to subject the fatty material and caustic solution to thorough mixing and intense agitation very shortly after they are contacted. Many different types of apparatus are adapted to accomplish such mixing, e. g., a colloid mill into the inlet end of which the'proportionedstreams'offatand caustic are introduced and from the outlet end of which the reaction productisremoved. While such apparatus produces satisfactorycontactbetween the reactants, any variation in the ratio of feed rates, e. g., cyclic variation inherently introduced by the operation of the prop'ortioning device, is not'averaged out but persists in the reaction product.

It is a feature of the present invention,"in its preferred form, to overcome the effect of cyclic variation in the feed rate ratio "and this isaccomplished by recirculating the 'reactionprodnot in the reaction chamber so that the average "of comparable volume.

shape. chamber in an axial section, and in cross-section lar.

time of retention in the recirculating mass of a differential portion of the streams of material introduced is longer than the period of cyclic variation. Preferably the contactor comprises a closed reaction chamber in which the materials may be kept under substantial pressure. This mass of material in the reaction chamber is caused to flow in a closed path. At least in one zone in said path the mass is subjected to disruptive shearing attended by violent agitation. The fatty material and caustic which are to be reacted are continuously forced into this circulating mass, preferably immediately in advance of a position atwhich the mass is subject to the disruptive shearing and violent agitation.

The fatty material andcausti'c which are pumped under pressure into the reaction chamber displace therefrom a quantity of reacted material The point of withdrawal preferably is so located in the cycle of flow as to permit the maximum practical period of contact betweenthe reactants before the material is withdrawn from the reaction chamber and, in any event, the point of introduction of the reactants "and the point of withdrawal of the reaction mass are at opposite sides of the position where the mass is subjected to disruptive shear and violent agitation.

A suitable type of apparatus in which the material may be reacted in accordance with the process of the present invention is illustrated in Fig. 5.

The contactor Bil comprises a casing which may be made in two parts, a head I anda body i52 suitably bolted together so as to form a pressure-tight reaction chamber of toroidal Fig. 5 shows the shape of the reaction the chamber is annular except for a short section-adjacent to the inlet orifice where it is circu- A draft tube I54 is supported in the reaction chamber by internal ribs I56 extending from a center cone I58 on the head section I50 to the draft'tube and by external ribs I60 extending'from the draft tube to the outer wall of the casing. These supporting ribs are elongated axially so as to serve as guide vanes in the reaction chamber.

The reactants are introduced into the reaction chamber through the center of the cone I58 where concentric passages are formed by the pipes I52 and 64, which pipes are connected respectively to feed lines 30 and 32 from the supply tanks for the fatty material and alkali solution. The ends of the concentric passages "are provided with nozzles I66 and I68, forming inlet orifices for the reactants.

The head I50 also is provided with an outlet port I10 leading to the soap line 6 I.

The body section I52 is provided with guide vanes I'I'Z preferably aligned with the ribs I56 and I60. The guide vanes 'I'T2 extend from a means now to'be described. It will be observed that the draft tube I54 terminates short of the ends of the reaction chamber to provide a closed "path for the recirculation of the mass of material in the reaction chamber as indicated by the arrows in Fig. 5.

'Mounted in suitable bearings I16 in thecenter 7 post I14 is-a shaft-I I8 driven by a motor (not shown). A propeller I is provided with a plurality of blades I82' on a hub I84 which is keyed to the shaft I18 by keys I86 and it is held in position on the shaft by a retaining plate I88 and lock nuts I90 screwed on the end of the shaft. A hemispherical cap I92 bolted to the end of the shaft by the machine screw I94 preferably is provided to assist in bringing the reactants which are introduced adjacent thereto into the stream of circulating material. The part of the apparatus indicated by reference character I96 may include a system for preventing leakage of materials from the reaction chamber around the shaft I18, but this forms no part of the present invention and, since such systems are well known to those skilled in the art, no further description thereof is necessary.

In the operation of the apparatus shown in Fig. the propeller I80 is driven at a suitable speed through the shaft I18 and the motor associated therewith while the fatty material and alkali solution are introduced in suitable proportioned amounts into the reaction chamber. The propeller blades I82 cause the fluid mass that fills the reaction chamber to flow in a closed path around the draft tube I54. The guide vanes I56, I 60 and I12 prevent rotation of the mass as a; whole around the center axis of the device. The material, however, as it flows past the guide vanes I56 is subjected at this point to intense shearing and agitation by the rotation of the propeller blades I82 and the material under the influence of the propeller blades is given a rota tional movement in the same direction as the propeller. This sudden change in direction of fiow from axial to rotational sets up a high rate of shear (velocity gradient), disorganizing the mass and assuring thorough mixing and intimate contact. High rate of shear is similarly set up after the material passes through the propeller blades where the direction of flow changes rapidly from the rotational to the axial direction in passing between the guide vanes I12. More than one propeller may be used, if desired, with either stationary vanes between the propellers or different directions of rotation to provide more than one zone of high rate of shear in the cycle of flow, although satisfactory results in practice have been obtained using a contactor of substantially the structure illustrated. The material in the reaction chamber is maintained under pressure which is readily controlled by the back pressure in the soap outlet line. This back pressure may be suificient by reason of the diameter and/or length of the pipe itself or, if necessary, a back pressure control valve maybe provided.

The capacity of the reaction chamber is so dimensioned that the average time of retention in the recirculating mass of a differential portion of the streams of fatty material and alkali is greater than the period of cyclic variation in the proportioning device. By this expedient the variation in the ratio of fatty material to caustic which is inherent in automatic proportioning devices is averaged out so that the quality of the soap leaving the reaction chamber through outlet I will have uniform and constant quality when the proportioning device has once been properly set for the saponification value of the fatty material and the concentration of the alkali solution being used.

The introduction of the fatty acids and alkali solution into a mass of the reaction product through whichthe reactants are finely dispersed in intimate contact has another important advantage of accelerating the rate of the neutralization or saponification reaction. The reaction product acts as an autocatalyst for the reaction, thus shortening the tim required for complete neutralization as compared with systems in which thereis no recirculation of the reaction product. High output capacity for equipment of a given size is thus made possible by the present invention.

The following specific example will illustrate the operation and advantages of the invention as thus far described.

Example Red oil which is maintained in a storage tank at a temperature suitable for pumping, e. g., about 110 F.,, is pumped into the supply tank so as to maintain the level inthe tank substantially constant. This oil is then continuously circulated through the heater at the rate of about 20 gallons per minute where it is heated to a temperature of about 140 F. At this temperature the oil has a specific gravity of about 0.87. A portion of the circulating stream which is automatically'maintained at the desired temperature by the temperature controlling device and associated parts is pumped at a rate of about 3,125 pounds per hour into the contactor 60.

Caustic soda solution (25% NaOI-I and 75% R20) is maintained at a constant temperature of F. by circulation through the heater at the rate of about 10 gallons per minute. A

portion of the circulating stream of caustic is bled off and pumped simultanteously with the red oil at a rate of about 1,875 pounds per hour into the contactor. The caustic solution at this concentration and temperature has a specific gravity of about 1.29. The caustic and fatty acids react rapidly to form soap of about 30% moisture content which is forced from the contactor by the pressure of the incoming fluids at a rate of about 5,000 pounds per hour. The pressure in the contactor is about '75 pounds per square inch gauge.

The contactor, which has a reaction chamber of about 5 gallons capacity, is found to be suitable for making soap at the rate specified. The average time of contact of differential portions of the streams of red oil and caustic between the time of introduction and withdrawal is of the order of about 30 seconds within which time the saponification reaction goes to completion. The proportioning device used to control the flow of the oil and caustic solution is an Askania ratio controller in which the period of cyclic variatiTm is considerably less than 30 seconds, e. g., about 5 seconds. The soap flowing through the line is found to be typical kettle soap of excellent quality, having uniform and constant free alkali content of about 0.10% as NazO.

For large scale continuous production of soap in accordance with the present invention, it is preferred to determine the quality of the soap produced, particularly the free alkali content, and use this determination automatically to control the setting of the proportioning device to take care of variations in the feed such as a change in the saponification value of the fatty material, a change in the concentration of the solution of the saponifying agent, or, when using a volumetric proportioner if temperature variation of either of the feed materials is permitted, a change in the specific gravity of either or both feed materials. Such control preferably isaccomplished by employing means for generating an electrical potential related to tire free alkali in the soap flowing through the discharge line and utilizing this electrical potential, continuously or periodically, for adjusting the proportioning means. The electrical potential may be generated in a number of different ways. One way, for example utilizing a pH control meter, comprises diverting a portion of the stream of soap flowing from the contactor and continuously mixing distilled water therewith to obtain an aqueous soap solution of known concentratiOn, e. g., about 3.5 grams of anhydrous soap per 100 grams of water. The temperature of this solution should be held at a constant value, e. g., about 40:1 C. as it flows over the electrodes of the pH control meter. Using a conventional glass electrode uncorrected. for sodium ion in combination with a regular saturated KCl-calomel electrode, it has been found that a variation in pH of about 0.1 pH unit in this solution corresponds to a change in alkali content of about 0.03% as NazQ in the soap urider control. Such a change in the generated electrical potential from a predetermined value can be used to modify the setting of the flow ratio controller so as to correct for any excess or deficiency in the desired free alkali content. This may be accomplished by electrical, pneumatic, hydraulic, or other means, as those skilled in the art are aware. This system can be utilized to control the free alkali content of soap having any desired percentage of moisture.

Instead of using a pH control meter, a portion of the soap stream leaving the contactor can be treated with an indicator to obtain a colorimetric value related to free alkali content, and by passing light of suitable wave length through the indicator-treated material onto a photoelectric cell, a potential is generated which also is related to the free alkali content of the soap. That potential may be utilized as the motive force to operate electrical, pneumatic, hydraulic or other means to vary the flow rate ratio of the proportioner to correct for any deviation from the predetermined desired free alkali content.

Another way of generating a potential related to the free alkali content of the soap without diluting the soap is described in the Miles et al. U. S. Patent No. 2,345,465, and this potential may be used in the same manner as described hereinabove to vary the flow rate ratio of the proportioner as required to keep the free alkali content of the soap within predetermined narrow limits.

The soap produced by the present invention may be further processed in any desired manner. It is customary to add other ingredients to soap, e. g., builders, perfume, whitening agents, etc. These ingredients may be added batchwise to soap obtained from the contactor, but it is preferred to add such ingredients continuously to the stream of soap. A suitable apparatus for adding such ingredients to the stream of soap is illustrated in Fig. 4. In this figure, the reference numeral 200 represents a supply line for fatty material, 202 is a supply line for caustic solution, and 204 is a proportioning device (e. g., a Bowser proportioner) for controlling the flow of these fluids into the contactor 206. The soap line 208 leading from the contactor 206 connects the reaction chamber with a continuous crutcher 2H] into which the additional material simultaneously is introduced through a supply line 2|2. The flow of the additional material through the line 2| 2 is also controlled by the proportioning device 204. The continuous crutcher 2H) may have a structure similar to that illustrated in Fig. 5 of the drawing for the reaction chamber, but the invention is not limited to the use of similar devices. After thoroughly mixing the materials in the crutcher so as to produce a uniform composition, the soap is withdrawn through a line 214 for finishing. The soap, for example, may be pumped to a tower for spray or flash drying to produce granular or particulate products; or it may be framed to produce framed cakes of soap; or it may be fed to continuous cooling and milling devices for'the production of bar soap, or to a drum or other dryer for the production of flakes which may be used in this form or treated in the usual way to produce milled soaps.

The present invention has been particularly described in connection with the saponification of fatty acids with aqueous sodium hydroxide of such concentration as to produce soap of about the composition of kettle soap, but the method. and apparatus of the invention are not limited to the saponification of free fatty acids, or to the use of caustic soda, or to the production of soap of approximately 30% water content. The invention contemplates the saponification of other materials such as fats and oils from animal and/or vegetable sources in the form of glycerides or as monohydric alcohol esters of fatty acids such as the methyl and/ or ethyl esters of coconut oil, palm kernel oil, tallow, etc., either singly or in combination. Any saponifying agent may be used, such as caustic soda, caustic potash, alkali carbonates, ammonium hydroxide, etc. The moisture content of the soap produced may vary over a wide range, it being necessary, however, to correlate the input temperature of the reactants with the moisture content so that the reaction product has suitable fluidity.

Although the invention has been described in connection with certain specific embodiments of the apparatus and method, modifications and variations may be resorted to without departing from the scope of the invention as defined in the following claims.

I claim:

1. A continuous process of making soap comprising establishing a mass of fluid soap in an elongated reaction chamber of annular crosssection, circulating said fluid soap axially in said. chamber in one direction adjacent to the inner wall thereof and axially in the opposite direction adjacent to the outer wall thereof, subjecting the circulating stream of soap in at least one zone to disruptive shear, continuously introducing separate streams of fatty material and alkali solution into said circulating stream of soap adjacent to, and in advance of, said zone of disruptive shear, and continuously withdrawing a stream of soap from said circulating stream adjacent to, but in advance of, the place of introduction of said fatty material and caustic.

2. The process of making soap continuously comprising maintaining a mass of soap under continuous flow around a closed path, continuously dispersing proportioned amounts of fatty acids and alkali without premixing in said circulating mass, and continuously removing a stream uously introducing saponifiable material and a 13 saponifying agent under pressure into said flowing mass, and permitting the introductionthereof continuously to displace from said mass a stream of soap.

4. A continuous process of making soap comprising establishing a mass of fluid soap under superatmospheric pressure, causing said mass to flow in a cycle, subjecting said mass in at least one zone in said cycle to violent agitation, continuously forcing into said flowing mass proportioned streams of saponifiable material and a saponifying agent, said streams being subject to cyclic variation in proportion, permitting the introduction of said proportioned streams continuously to displace from said mass a stream of soap, and maintaining the average time of retention in said mass of a differential portion of the streams of material introduced greater than the period of said cyclic variation.

5. In the process of making soap by the continuous introduction of proportioned streams of saponifiable material and a saponifying agent into a reaction chamber and the continuous withdrawal of soap from said chamber, the proportioning of said streams being subject to cyclic variation, the improved method of producing soap of substantially constant quality which comprises forming and continuously maintaining in said chamber a mass of soap under superatmospheric pressure, causing said mass to flow in a closed path in said chamber, subjecting said mass in at least one zone in said path to disruptive shear, continuously forcing into said mass the proportioned streams of saponifiable material and saponiIying agent, permitting the introduction of said proportioned streams continuously to displace a stream of soap from said mass, maintaining the average time of retention in said mass 01 a difterential portion of the streams of material introduced greater than the period of said cyclic variation, and automatically controlling the proportioning of said streams to maintain the free alkali content of the stream of soap substantially constant at a predetermined value.

6. In the process of making soap by the continuous introduction of proportioned streams of fatty acids and alkali solution into a reaction chamber and. the continuous withdrawal of soap therefrom, the proportioning of said streams being subject to cyclic variation, the improved method of producing soap of substantially constant quality which comprises forming and continuously maintaining in said chamber a mass of soap under superatmospheric pressure, causing said mass to flow in a closed path in said chamber, subjecting said mass in at least one zone in said path to disruptive shear, continuously forcing into said mass at closely adjacent points adjacent to, but in advance of, said zone of disruptive agitation the proportioned streams of the fatty acid and alkali solution, permitting the introducing of said proportioned streams continuously to displace a stream of soap from said mass, maintaining the average time of retention in said mass of a differential portion of the streams of material introduced greater than the period of said cyclic variation, and automatically controlling the proportioning of said streams to maintain the free alkali content of the stream of soap displaced from the mass at substantially a constant predetermined value.

LOWELL A. LEDGET'I'.

REFERENCES CITED The following references are of record in the 

1. A CONTINUOUS PROCESS OF MAKING SOAP COMPRISING ESTABLISHING A MASS OF FLUID SOAP IN AN ELONGATED REACTION CHAMBER OF ANNULAR CROSSSECTION, CIRCULATING SAID FLUID SOAP AXIALLY IN SAID CHAMBER IN ONE DIRECTION ADJACENT TO THE INNER WALL THEREOF AND AXIALLY IN THE OPPOSITE DIRECTION ADJACENT TO THE OUTER WALL THEREOF, SUBJECTING THE CIRCULATING STREAM OF SOAP IN AT LEAST ONE ZONE TO DISRUPTIVE SHEAR, CONTINUOUSLY INTRODUCING SEPARATE STREAMS OF FATTY MATERIAL AND ALKALI SOLUTION INTO SAID CIRCULATING STREAM OF SOAP ADJACENT TO, AND IN ADVANCE OF, SAID ZONE OF DISRUPTIVE SHEAR, AND CONTINUOUSLY WITHDRAWING A STREAM OF SOAP 